This invention relates to improvements in those types of vacuum pump known as turbomolecular pumps, and more particularly relates to a "hybrid" or compound pump having a turbomolecular stage and a stage of different operational mode for improving the operating range of pressures and throughput.
A standard turbomolecular pump includes a rotor comprising arrays of (normally) angled blades arranged for rotation at high speed, for example up to sixty thousand revolutions per minute, between alternately arranged arrays of stationary blades of a stator; generally the blades of the stator are inclined in the opposite direction to those of the rotor. In such pumps, gas is received from a high vacuum chamber, compressed and delivered to a backing pump inlet, normally that of a two stage rotary pump. The backing pump is required in that the turbomolecular pump normally operates with exhaust pressure up to about 10.sup.-1 mbar and the use of the backing pump can provide backing pressures in this region and deliver pumped gas to the atmosphere.
Compound pumps are known in which the turbomolecular stage and a further stage are present in a single pump. The further stage may, for example, be a screw rotor stage or a spiral groove stage or certain types of other molecular drag stage. Nevertheless, there remains a need for improved hybrid pumps.
The present invention is concerned with the provision of a hybrid pump in which the further stage, i.e. in addition to the turbomolecular stage, has been found to be particularly useful in conjunction with the turbomolecular stage itself.